In the existing literature, IRS is mainly employed as a passive relay near the transmitter/receiver to assist their communication [1]}, [2]}.
Different from the conventional half-duplex amplify-and-forward (AF) and decode-and-forward (DF) active relays, IRS operates in full-duplex with passive signal reflection only, thus incurring no amplification/processing noise, and achieving high spectral efficiency at low hardware/energy cost [1]}, [2]}, [5]}.
Recently, to further improve the wireless relaying performance, new hybrid active/passive relay systems have been proposed in [6]}, [7]}, [8]}, where IRS is employed to enhance the channel gain of the transmitter-(active) relay and/or relay-receiver links.
However, these works assumed a single IRS (or multiple IRSs in close proximity) deployed at fixed location, but did not study the effect of IRS deployment (i.e., IRS elements partition/placement) on the system performance.
For example, it remains unknown whether the conventional strategy by deploying IRS near the transmitter/receiver is still optimal for the IRS-aided relay system, and whether it is beneficial to divide one single IRS into multiple smaller-size IRSs and place them near the transmitter, receiver, and/or relay.
